SSINS No.: 6835
IN 86-50
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
June 18, 1986
Information Notice No. 86-50: INADEQUATE TESTING TO DETECT FAILURES OF
SAFETY-RELATED PNEUMATIC COMPONENTS OR
SYSTEMS
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP).
Purpose:
This notice is being provided to alert recipients to a potentially
significant problem pertaining to inadequate testing practice relating to
air operated valves. The NRC expects that recipients will review this notice
for applicability to their facilities. However, suggestions contained in
this notice do not constitute NRC requirements; therefore, no specific
action or written response is required.
Past Related Correspondence:
Information Notice No. 82-25, "Failures of Miller Actuators Upon
Gradual Loss of Air Pressure," July 20, 1982
Information Notice No. 85-35, "Failure of Air Check Valves to Seat,"
April 30, 1985
Information Notice No. 85-84, "Inadequate Inservice Testing of Main
Steam Isolation Valves," October 30, 1985
Information Notice No. 85-94, "Potential for Loss of Minimum Flow
Paths Leading to ECCS Pump Damage During a LOCA," December 13, 1985
Description of Circumstances:
The NRC has reported previously on instances where safety-related equipment
failed to operate as intended when non-safety-related pneumatic systems were
unavailable (IE INs 82-25 and 85-35). In these situations, main steam
isolation valves and containment isolation valves failed to operate properly
when control air pressure decreased slowly rather than rapidly as would be
expected for an air line break. In the case of IN 85-35, the fault was
exposed by a loss of offsite power test, and in the case of IN 82-25, the
fault was exposed by a preoperational test designed to simulate a slow air
leak. In both cases,
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IN 86-50
June 18, 1986
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the components in question--an accumulator isolation check valve (IN 85-35)
and pneumatic selector valves (IN 82-25)--were not tested adequately.
Several recent events have indicated continuing problems of similar nature.
These events are discussed below.
On February 13, 1986, the licensee at Turkey Point Unit 3 first reported to
the NRC a concern that the component cooling water (CCW) system might fail
to meet its functional requirements for a design-basis accident. One part of
the concern involved the CCW heat exchanger outlet control valve. This valve
regulates flow of intake cooling water (ICW) to this heat exchanger. Loss of
control air, coincident with a loss of offsite power, a valid engineered
safeguards features (ESF) actuation signal, and a loss of an emergency
diesel generator (EDG) would cause this valve to fail closed. If this
happened, the CCW heat exchanger would not receive sufficient flow of ICW.
This situation was discovered during a design review of the ICW system.
Earlier disclosure might have been possible if ICW operation had been
considered or tested with non-safety-related control air secured, coincident
with loss of electrical power.
On January 7, 1986, the licensee at Robinson Unit 2 reported a concern with
the air-operated valves in the safety injection (SI) pump minimum-flow
recirculation line from the pump discharge to the refueling water storage
tank (RWST). This concern evolved from review of IN 85-94. Two such valves
had been inserted in series in this line and had been designed to fail
closed on loss of non-safety-related air or loss of electrical power to the
valves. The purpose of the valves is to protect the RWST (outside
containment) from highly radioactive reactor coolant during the long-term
circulation phase of accident recovery. In the event of SI initiation under
small-break loss-of-coolant-accident conditions concurrent with closure of
either of these valves, the SI pumps would be operating with no flow until
reactor pressure decreased below their shutoff head. This would damage the
SI pumps after only a short time. The licensee's remedy was to put
mechanical blocks on the air operators so the valves would fail as-is
(open). Again, if SI operation had been considered or tested with
non-safety-related control air secured, the fault might have been disclosed
earlier.
On December 9, 1985, the licensee at Catawba Unit 2 reported finding that
one of the two valve closure springs was missing on one of the pressurizer
power-operated relief valves (PORVs). Thus, with loss of air the valve would
not have closed against system pressure. The other two PORVs had their
normal complement of springs. The valve with the missing spring had been
found satisfactory in preoperational tests. During the preoperational loss
of air test, the valve closed because system pressure was not present;
during the hot functional test, the valve closed because actuator air
pressure was present. This is clearly a case in which a fail safe valve was
tested without all actuator power secured (IN 85-84).
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IN 86-50
June 18, 1986
Page 3 of 3
No specific action or written response is required by this information
notice. If you have any questions about this matter, please contact the
Regional Administrator of the appropriate regional office or this office.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: Vern Hodge, IE
(301) 492-7275
Attachment: List of Recently Issued IE Information Notices